We aim to recruit 50 neonates and infants under the age of 3 months who have been prescribed Ciprofloxacin as inpatients for suspected or proven infection. They will be recruited over 2 years from the neonatal unit at Liverpool Women's NHS Foundation Trust and Alder Hey Children's NHS Foundation Trust. Consent will be requested for babies to have more detailed investigation to see if there if genetic factors affect the way the body handles ciprofloxacin.